Is it normal to mourn the death of someone you never met?

Last March a wonderful girl passed away at my school. I didn't know her since she was a year younger but I know she was so wonderful and full of life. Everyone obviously misses her terribly and I feel so helpless because she can't come back. The morning she passed I wasn't at school, nor the next few days for unrelated reasons. But apparently everybody was a mess and I felt almost embarassed! Even now, seeing how much everyone is doing to honor her makes me feel so sad as well. I cried so much when what should have been her 18th birthday came around, yet her closest friends celebrated and had at least a facade of happiness. So, is it normal to still feel sadness towards the death of practically a stranger over half a year later?